THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

Fault detection and diagnosis in power transformers: a comprehensive review and classification of publications and methods

Review on asset management of power transformer by diagnosing incipient faults and faults identification using various testing methodologies

A power transformer is one of the most critical and expensive assets in electric power systems. Failure of a power transformer would not only result in a downtime to the entire transmission and distribution networks but may also cause personnel and environmental hazards due to oil leak and fire. Hence, to enhance a transformer’s reliability and extend its lifespan, a cost-effective and reliable condition monitoring technique should be adopted from day one of its installation. This will help detect incipient faults, extend a transformer’s operational life, and avoid potential consequences. With the global trend to establish digital substation automation systems, transformer online condition monitoring has been given much attention by utilities and researchers alike. Several online and offline condition monitoring techniques have been recently proposed for oil-immersed power transformers. This paper is aimed at providing a state-of-the-art review for the various condition monitoring technologies used for oil-immersed power transformers. Concept of measurements and analysis of the results along with the future trend of condition monitoring techniques are presented.

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Oil-Immersed Power Transformer Condition Monitoring Methodologies: A Review

Some industrial incidents are attributed to insulation degradation of electrical assets. The leakage current can be a crucial indicator for online insulation monitoring of asset. To realize per-phase monitoring, the measurement accuracy of milliampere-level leakage current is limited by the strong load current noises. This article proposes an advanced current sensor with a dual-core topology based on differential-mode (DM) measurement. An analytical model of magnetic field of the dual-core sensor is originally presented. It helps clarify the significances of the inner core in filtering noises and reducing the influence of system operation and cable positioning. Then, a comprehensive design procedure is fully investigated by selecting the optimal position and approach for magnetic field detection, and a high-speed and low-noise signal conditioning circuit is presented. The proposed current sensor is tested in the laboratory. Experimental results indicate that measurement errors can remain within 0.1mA in the testing scope, where the load current is up to 100A and the DM current varies from 0-7mA. The proposed sensor is further validated with superior performance compared with two commercial industrial sensors. The contribution of this article lies in providing the analytical analysis and design of a novel DM current sensor for leakage current measurement, which achieves online per-phase insulation monitoring for industrial electrical assets.

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Analytical Analysis and Design of an Advanced Differential-Mode Current Sensor for Insulation Monitoring for Industrial Electrical Assets

This paper aims to evaluate the capacitance and the dielectric dissipation factor (DF) of brand new distribution transformers tested in the past two years at LAT-EFEI High Voltage Laboratory. Evaluation proposed consists to classify the capacitance between windings and between the windings and the ground, as well as the DF, according to the rated power, voltage class and number of phases. The DF analysis is based on IEEE Std. C57.152 limits and it aims to infer the insulation quality prior its operation on distribution networks. The parameters measurements were carried out on 170 distribution transformers made in Brazil, using a Schering bridge. The measurements showed a considerable number of samples with DF greater than the limit for a good insulation's condition.

Evaluation of Capacitance and Dielectric Dissipation Factor of Distribution Transformers - Experimental Results

This paper aims at evaluating the lightning withstand voltage of cut-out fuses designed for overhead distribution lines of 15 kV and 25 kV. For this purpose, it is used the critical flashover voltage (CFO) and the V-t curves parameters. These two parameters are usually derived for 1.2 × 50 μs impulse shape, which represents overvoltages originated by direct lightning strikes on phase conductors or shield wires of transmission and distribution lines. In order to assess the lightning withstand levels with respect to induced overvoltages, it has been chosen five nonstandard impulse shapes with front and tail times of 0.5 × 5 μs, 0.5 × 20 μs, 1.2 × 10 μs, 3 × 16 μs and 5 × 50 μs. The standard impulse shape 1.2 × 50 μs results are also provided for the purpose of comparison with nonstandard ones. The tests for determining the CFO and V-t curves were performed on dry condition, for positive and negative polarities. The CFO and V-t curves results show an important issue considering lightning withstand of cut-out fuses. For both test methods and impulse shapes, the lowest withstand values are observed on negative polarity. Considering porcelain insulators and manual disconnectors for distribution systems, it means a change on the critical polarity with impacts on insulation coordination procedures.

Lightning withstand of medium voltage cut-out fuses stressed by nonstandard impulse shapes experimental results

Investigations, through a sample evaluation, aiming to evaluate the cause of the high-frequency oscillations presented by distribution transformers in impulse tests reveal that internal imperfections, such as cavities and floating particles, cause these oscillations.

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Investigation of High-Frequency Oscillation Discrepancies Presented by Distribution Transformers During Lightning-Impulse Voltage Tests

Lightning discharge activity causes overvoltages in the electric power system, which may result in damage to the equipment and apparatus of the system. The lightning incidence is divided into two types: direct strikes and side strikes [1–4]. Direct strikes are lightning discharges that directly hit the line, structure or equipment, resulting in overvoltages of higher amplitudes. However, they are less common than side strikes, which are discharges that occur near the electric system and induce overvoltages of lower amplitudes than direct strikes, but may also cause damage in the distribution network. In this way, many works have evaluated the effect of side strikes on the insulation of electric power system equipment [5–8].

Lightning withstand of medium voltage switches and cut-out fuses considering standard and nonstandard impulse shapes

a presente invencao compreende uma composicao de revestimento eletricamente condutora para utilizacao na industria eletroeletronica. a composicao de revestimento condutora inclui como nanomaterial nanoparticulas de grafeno disperso em agua que pode ser aplicado em uma superficie do substrato para formar uma pelicula fina com propriedades eletricas diferenciadas. o revestimento condutor pode tambem compreender um nanomaterial formado a partir de nanotubos de grafeno enxertados com um polimero contendo um grupo funcional que aumenta sua adesao ao substrato. por substrato entende-se uma superficie polirnerica, metalica ou cerâmica. a tinta eletrocondutiva apresentada nessa invencao, por sua composicao ecologicamente correta, e isenta de particulas metalicas e volateis orgânicos e possui desempenho similar ou superior aos produtos concorrentes disponiveis no mercado nacional e, ou internacional.

Gabriel Henrique de Faria

Papers

Evaluation of Capacitance and Dielectric Dissipation Factor of Distribution Transformers - Experimental Results

Lightning withstand of medium voltage cut-out fuses stressed by nonstandard impulse shapes experimental results

Investigation of High-Frequency Oscillation Discrepancies Presented by Distribution Transformers During Lightning-Impulse Voltage Tests

Lightning withstand of medium voltage switches and cut-out fuses considering standard and nonstandard impulse shapes

formulação sustentável de tinta eletrocondutiva